The setting rate of butter during the first 5 h after manufacture was found to be increased by a higher maximum temperature during working, e.g. 15 as compared with 12·5 °C, or by a temporary rise in temperature to 18 °C for 30 min after working. A temporary lowering of temperature to 7 °C for 30 min, however, had no effect. The amount of working did not affect setting rate except where more prolonged working resulted in a higher final temperature in the butter.

When temperature conditions during and after working were standardized, it was found that temperature of pasteurization in either a Vacreator or plate pasteurizer or the presence of clumped fat in the cream had no effect on setting rate. The setting rate, however, was increased by Vacreator treatment as compared with plate pasteurization of cream or by low-pressure homogenization of cream after plate pasteurization.

Microscopic examination of butter samples showed much fewer intact fat globules in butter from Vacreator-treated or homogenized cream than in that from platepasteurized cream.

It is suggested that Vacreator treatment or homogenization of cream affect the setting rate of butter by causing changes in the fat-globule membrane which, in turn, influence the type of crystallization in the fat globules and the stability of the globules.